After the Supreme Court heard arguments Nov. 1 in a complex Clean Air Act case, attorneys who faced the justices' questions didn't want to predict the outcome. A ruling in the case, Environmental Defense v. Duke Energy Corp., is expected by July.

Phillips Duke Power's attorney sees no way to predict how broadly the court ruling might be. Company says hourly rate standard should be used to measure plant emissions.

How broad might the decision be? "I don't think there's any way you can predict based on the way the questioning went," says Carter G. Phillips, who represented Duke Energy. "There were some questions that dealt with fundamental issues involving the statute. There were questions that dealt with minutia within the regulatory scheme."

The case involves Environmental Protection Agency "new source" rules under the clean air law that take effect when modifications to existing plants increase emissions of pollutants. At issue in the case is what definitions of "modifications" and "increase" should apply.

In 2000, the U.S. charged that Duke, by carrying out work at eight powerplants that resulted in higher emissions without getting a "prevention of significant deterioration" permit, violated the Clean Air Act. Duke disagreed. It won in district court and the Fourth Circuit federal appeals court. Duke says none of the modifications "increased any unit's capacity to emit pollutants," using an hourly rate. Environmental Defense appealed to the Supreme Court, contending the correct yardstick to apply is an increase in "actual" emissions in "tons per year."

Donahue Environmental Defense attorney says case is about intent of Congress in Clean Air Act. His side favors using "actual" annual volume to gauge emission increases after powerplant modifications.

Sean H. Donahue, Environmental Defense's attorney, told the high court the rule at issue is "clear on its face." Chief Justice John Roberts said, "That's an audacious statement," sparking laughter.

Environmental Defense says federal clean air rules can be challenged only in the D.C. Circuit appeals court. The Duke case came from the Fourth Circuit. Duke says it's not challenging the rules, but EPA's interpretation as reflected in the 2000 enforcement action.

After the oral arguments, Donahue said the case is about whether Congress' intent in setting up the new source program will be followed. He calls the clean air program, with its various acronyms, an "alphabet soup" that is "not easy even for people accustomed to very complex legal questions." "We're very optimistic that the court will get it right," he says, but makes no predictions. Says Duke attorney Phillips: "I will be surprised if you get a decision very soon."